Digested products of human stabilized fibrin with various proteases are useful as diagnostic markers in clinical diagnosis. For example, plasmin-digested products of human stabilized fibrin, which include p-DD/E as a base unit, and polymers or oligomers thereof (hereinafter sometimes referred to as D-D dimer or DD/E complex), are widely used as a diagnostic marker of disseminated intravascular coagulation (DIC). In a determination of the plasmin-digested products of stabilized fibrin in a biological sample, an agglutination of latex sensitized with a monoclional antibody specific to the plasmin-digested products of stabilized fibrin is generally used.
Deep vein thrombosis (DVT) is now in need of attention. DVT has not been greatly noted in Japan, but the number of patients suffering therefrom is increasing as the westernization of Japanese life style proceeds. A diagnosis or prediction of thrombosis or the presence of thrombi is extremely difficult, but the plasmin-digested products of stabilized fibrin is the most reliable marker for a DVT diagnosis (nonpatent references 1 and 2). Stabilized fibrin, which is generated by crosslinking fibrin during a coagulation process, is digested with plasmin to covert p-DD/E polymers or oligomers composed of the p-DD/E base unit, or p-DD/E. Therefore, the formation of thrombus and the secondary fibrinolysis may be monitored by detecting p-DD/E or the polymers or oligomers thereof. The measurement of the plasmin-digested products of stabilized fibrin is very useful in confirming the presence of thrombi.
Pulmonary embolism (PE), known as the economy-class syndrome, has come to the fore. PE is considered to be developed by blocking the blood flow with deep vein thrombi that pass through the inferior vena cava and pulmonary heart and reach a pulmonary artery. There is a report that the measurement of the plasmin-digested products of stabilized fibrin is useful in evaluating patients suffering from PE as well as those with DVT (nonpatent references 3 and 4).
A monoclonal antibody JIF-23 is known as a monoclonal antibody capable of specifically detecting the plasmin-digested products of stabilized fibrin (nonpatent reference 5). It is known that this antibody recognizes the N-terminal structure newly exposed in the D1 domain after liberating the N-terminal sequence consisting of amino acids 63-85 in the γ chain of the D1A domain in the plasmin-digested products of human stabilized fibrin therefrom. The formation of thrombus and the secondary fibrinolysis can be easily monitored by a measuring method capable of specifically analyzing the plasmin-digested products of stabilized fibrin contained in a biological sample using the antibody JIF-23. Such a measuring method is not particularly limited, but may be, for example, a latex agglutination method or an ELISA method.
A latex agglutination method is known in the clinical field as a commonly-used conventional method of measuring the plasmin-digested products of stabilized fibrin using the antibody JIF-23. The amount of the plasmin-digested products of stabilized fibrin is 0.4 μg/mL FEU in healthy persons according to nonpatent reference 6, and 15.2±18.5 μg/mL in patients suffering from DIC according to nonpatent reference 7. The plasmin-digested products of stabilized fibrin can be detected with the latex agglutination reaction using the antibody JIF-23 (sensitivity of detection=approximately 45 ng/mL) and, in fact, this method is commonly used in the clinical field.
The clinical cut-off value for DVT is 0.5 μg/mL FEU according to nonpatent reference 8. The diagnosis of DVT requires monitoring slight changes between values of healthy persons and patients in comparison with the diagnosis of DIC, and therefore, a more sensitive measuring method capable of accurately assaying the plasmin-digested products of stabilized fibrin in the normal range is desired.
As an ELISA method using an antibody that recognizes a neoantigen in the D domain of the digested products of stabilized fibrin, for example, MiniVidas (Biomerieux) is known (nonpatent references 8 and 11). It is reported in nonpatent reference 9 that the sensitivity in an ELISA method is higher than that in a latex agglutination, and thus, the ELISA method is useful in the diagnosis of DVT. Such an ELISA method with a high sensitivity is spreading to the clinical field as a method of measuring the plasmin-digested products of stabilized fibrin. For example, the detection sensitivity of the MiniVidas is approximately 45 ng/mL FEU.
The values and units as described above are based on the descriptions of the nonpatent references, and the units “μg/mL FEU” and “μg/mL” can be interconverted according to the following equation:1 μg/mL=2 μg/mL FEUwherein the value “2” is an approximate value (nonpatent reference 10).[non-patent reference 1] Thrombosis and Haemostasis, Germany, 1994, vol. 71, p. 1-6[non-patent reference 2] Quality Journal of Medicine, United Kingdom, 1997, vol. 90, p. 437-442[non-patent reference 3] Thrombosis and Haemostasis, Germany, 1999, vol. 81, p. 493-497[non-patent reference 4] Thrombosis and Haemostasis, Germany, 2000, vol. 83, 191-198[non-patent reference 5] Excepta Medica, Amsterdam, Netherlands, 1990, p. 43-48[non-patent reference 6] U.K. National External Quality Assessment Scheme for Blood Coagulation, Report on Survey 142, United Kingdom, May, 2004[non-patent reference 7] ANNALES DE BIOLOGIE CLINIQUE, France, 1988, vol. 46, p. 730-733[non-patent reference 8] Biomerieux Vidas D-Dimer Package Insert, U.S.A., September, 2003, 008120-4[non-patent reference 9] Annals of Internal Medicine, U.S.A., 2004, p. 589-602[non-patent reference 10] Journal of Thrombosis and Haemostasis, United Kingdom, 2005, p. 377-384[non-patent reference 11] British Journal of Haematology, United Kingdom, 2004, p. 15-25